1. Field of the Invention
This invention relates in general to orthodontics and more particularly to methods and kits for for providing pontics in orthodontic appliances.
2. Description of the Background Art
Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as xe2x80x9cbraces.xe2x80x9d Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and O-rings. After they are bonded to the teeth, periodic meetings with the orthodontist are required to adjust the braces. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time-consuming process requiring many visits to the orthodontist""s office. Moreover, from a patient""s perspective, they are unsightly and uncomfortable. Consequently, alternative orthodontic treatments have developed. A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such an appliance may be comprised of a thin shell of elastic material, referred to as an xe2x80x9calignerxe2x80x9d that generally conforms to a patient""s teeth but is slightly out of alignment with the initial tooth configuration. Placement of an aligner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually moves the teeth through a series of intermediate arrangements to a final desired arrangement. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT application WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
Systems of preformed aligners employing technology described in U.S. Pat. No. 5,975,893, are commercially available from Align Technology, Inc., Santa Clara, Calif., under the tradename Invisalign(copyright) System. Align Technology, Inc., is the assignee of the present application. The Invisalign(copyright) System relies on designing and fabricating the aligners to be worn by the patient throughout treatment. The design of the aligners relies on computer modeling of a series of successive tooth arrangements, and the individual aligners are designed to be worn over the teeth and to reposition the teeth to each of said tooth arrangements. Usually, the set of aligners which is designed and fabricated at the outset of the treatment is able to successfully reposition the teeth to a final desired arrangement.
With the Invisalign(copyright) System, as well as with other conventional orthodontic treatment systems, it is sometimes necessary to extract one or more teeth prior to tooth repositioning. At present, the Invisalign(copyright) System does not provide for filling in the space or void which remains within the aligner after the tooth is extracted with a structural component such as an artificial tooth which is commonly referred to as a dental pontic.
The design and fabrication of dental pontics are described in U.S. Pat. Nos. 6,186,790; 6,050,820; 6,049,743 and 5,613,845, the full disclosures of which are incorporated herein by reference. Currently, dental professionals trained in the use of the Invisalign orthodontic system are using a variety of materials and techniques known in the art to fabricate dental pontics which can be worn in the aligner extraction site(s). The most commonly employed materials are tooth-shaded dental composites typically used to repair carious lesions or fabricate provisional (temporary) crowns and bridges. These materials consist mainly of a polymer matrix and dispersed reinforcing inorganic filler particles. Typical polymers used are based on dimethacrylate such as Bis-GMA or urethane dimethacrylate (UDMA). Quartz, lithium aluminum silicate and barium, strontium, or zinc glasses have been commercially distributed as fillers. Typically these materials are packaged as a two-paste (base/catalyst) system. The polymer matrix may be visible light curable, self-curing, dual curing, and vacuum, heat and pressure curable compositions as well as any combination thereof. A popular method for mixing and dispensing these materials involves the use of an automix system whereby a dispensing gun is utilized to dispense the base and catalyst, which are in separate cartridges, through a mixing cannula directly into the extraction site. Commercial examples of the autopolymerizing composites are Luxatemp Plus (DMG/Zenith), Integrity (Dentsply/Caulk), Protemp Garant (ESPE) and Turbo Temp (Danville Engineering). Alternatively light cured composites may be used to fabricate dental pontics. Commercial examples of light cured composites are Revolution (Kerr), Star-Flow (Danville Engineering), and Tetric (Vivadent). Other useful dental composite materials are based on the methyl methacrylate polymer. Such acrylic polymers are well known and commercially available for example as Jet Tooth Shade self-curing acrylic resin by Lang Dental.
Although dental composites have been used to fabricate dental pontics for the Invisalign system there remain two important disadvantages to using these materials. First the ability of these materials to bond to the aligner thermoplastic is poor and second these materials are very stiff and non-flexing. These characteristics significantly compromise retention of the pontic in the aligner especially if it is subjected to torsional or flexing forces such as when the aligner is either being inserted or removed from a patient""s mouth or while the patient is cleaning their aligner using a cleaning device such a toothbrush or denture brush.
While it has been proposed to paint or color a portion of the aligner which overlies the void (see co-pending application Ser. No. 09/454,278, the full disclosure of which is incorporated herein by reference), partial coloring of the aligner can affect the light transmitting properties and be unaesthetic and the lack of any underlying structure can weaken or lessen the resilience of the aligner and limit its effectiveness.
For these reasons, it would be desirable to provide methods, systems, and kits for modifying an aligner to accommodate patients who have had teeth extracted prior to treatment with an aligner or other polymeric shell orthodontic appliance. It would be particularly desirable if the methods would permit an orthodontist or other clinician to modify an aligner or other orthodontic appliance in the professional office, rather than having the modification done at the time of fabrication or at an off-site location. It would be further desirable still if the aligner could be modified by the treating clinician, fitted with the patient, and further modified if necessary for patient comfort or other reasons. The resulting modified aligners or other orthodontic appliances should be esthetically pleasing, and preferably should mask the absence of an underlying tooth while the aligner or other appliance is worn. At least some of these objectives will be achieved by the inventions described hereinafter.
U.S. Pat. No. 5,975,893, and published PCT application WO98/58596, have been described above. Co-pending application Ser. No. 09/454,278, which has been published as WO99/028,228, relates to the fabrication of aligners which have been colored to cover a void left where teeth have been removed. The full disclosures of each of these patents and pending applications are incorporated herein by reference.
The present invention provides methods and kits for forming a pontic in a polymeric shell dental appliance, such as the Invisalign(copyright) System aligners described above. In addition, the present invention provides for methods of using such modified aligners for treating patients having gaps between adjacent teeth, where the gaps resulted from prior tooth extractions or other causes. In addition to the esthetic improvement, i.e., the voids or empty spaces between teeth will be generally invisible, it is believed that the pontics may reduce the tendency of teeth to collapse inward toward each other as the teeth are moved to close the gaps during the orthodontic treatment. In the case of the Invisalign(copyright) System, successive aligners which are used to treat an individual patient can each be separately modified, with the pontic placed in a gap between adjacent teeth being reduced in size as the treatment progresses and the gap is gradually closed.
According to a first aspect of the present invention, a method for forming a pontic in a polymeric shell dental appliance, such as an Invisalign(copyright) System aligner, comprises providing a polymeric shell dental appliance of the type which is removably placeable over a patient""s dentition. The shell will have a concave trough or cavity which conforms to the teeth when the appliance is placed or worn over the dentition. When the polymeric shell is worn, the treating clinician can determine the location in the appliance trough where a tooth is missing. The treating clinician will usually note the location on the appliance and further determine the width and shape of the gap between the teeth. Optionally, in the case of the Invisalign(copyright) System aligners, the aligner will have been shaped or otherwise modified to indicate the location where the gap will occur. If not, the treating clinician can simply mark the aligner or take other appropriate steps to determine the location of the space within the trough.
After the space (or spaces) is determined, the pontic is formed by filling the spaces(s) within the trough with a material that resembles a tooth. While it would be possible to shape a cured material into the desired geometry to be placed within the appliance trough, it will be much more convenient to fill the location with a relatively viscous but flowable and flexible material which can fill and conform to the interior volume of the target location within the appliance trough. Optionally, an adhesive or other treating material will be coated on the target location prior to filling with the pontic material. The flowable pontic material will then be cured to form the final pontic. Optionally, the shape of the pontic can be modified using spatulas (while it is still workable) and/or knives (after it has cured). Preferably, the pontic will be shaped so that it fills substantially the entire gap between adjacent teeth and extends down to the gingiva, without intruding upon the gingiva when the aligner or other appliance is worn.
In a specific embodiment of the present invention, curable silicone compositions, especially the addition-curable silicone rubber compositions known in the art are employed to form an elastomeric, flexible polyvinylsiloxane (PVS) dental pontic. Typically these polyvinylsiloxane materials are formed from a two component curable silicone prepolymer system. A first component, which is referred to as a xe2x80x9cBase Pastexe2x80x9d, typically contains a vinylorganopolysiloxane dispersion, an organo hydrogen-polysiloxane, inorganic fillers and other additives well known in the art. The second component of this two-part composition is referred to as a xe2x80x9cCatalyst Pastexe2x80x9d and typically consists of a second portion of the vinyl polysiloxanes, polymerization initiators, accelerators, cross-linking agents and other additives well known in the art. The base and catalyst may either be hand mixed and delivered to the appliance trough using a spatula or application syringe or a mixing device such as an auto-mix cartridge commonly used for impression materials may be employed to combine the proper volumes of base and catalyst. The tip size of the nozzle can be selected to provide a desired ribbon of material to be delivered to the appliance trough. Preferably, the tip of the nozzle will be held beneath the surface of the PVS as it is being dispensed within the appliance trough. By providing applicators having different tip diameters, the size of the material ribbon and the pontic can be selected by the treating physician.
Another class of curable silicone rubbers useful in forming elastomeric dental pontics are the condensation reaction silicones. Condensation silicones are supplied as either a paste and liquid or as two pastes. Typically the base paste consists of a silicone polymer with terminal hydroxy groups and a filler and the catalyst paste consists of a cross-linking agent (organohydrogen siloxane) and an activator such as dibutyl-tin dilaurate. On mixing the two pastes react by a condensation reaction causing cross-linking. Typically the setting reaction produces a gas such as hydrogen or an alcohol.
Prior to delivering the curable silicone rubber, an adhesive is applied to the aligner segment corresponding to the site of the missing tooth to enhance the bond between the PVS pontic and aligner thermoplastic.
After sufficient material has been dispensed to form the pontic, the treating clinician may optionally shape or form the pontic as desired, typically using conventional shaping tools, such as spatulas. The material will then be cured. In the case of PVS, curing will typically occur after five to ten minutes at room temperature but anybody skilled in the art can vary the material composition to allow for curing times  less than 60 seconds or as long as 24 hours. If it is desired to expedite curing, the PVS material may be gently warmed, e.g., held under a warm water stream. After curing, shaping or trimming of the pontic may be performed using a knife, abrasive instrument, or the like.
Non-toxic, inorganic iron oxide pigments may be incorporated in the PVS polymer to provide for a tooth-colored shade for the finished pontic. Optionally, a range of tooth-colored PVS resins may be provided in a kit allowing the clinician to select a color that best matches patient""s teeth. In a second aspect of the present invention, kits are provided comprising components of the system useful for performing the methods described above. In particular, the basic kit would include a curable, toothshaded PVS resin material such as described above in combination with instructions for use setting forth a method for forming the pontic within the trough of an aligner or other thin polymeric appliance having a trough or cavity which is removebly placed over teeth. In particular, the instructions will set forth a first step of determining the location in the trough where a tooth is missing from the patient""s dentition, and a second step comprising filling the location with the filler so that the material resembles a tooth when the location is filled.
Optionally, the kit may further include other components, such as an adhesive for coating an interior surface of the appliance trough at the location to be filled. When an adhesive is supplied, the kit will typically also include a brush, sprayer, or other applicator for applying the adhesive to the appliance trough. The kit may still further comprise one or more nozzles for use with a filler applicator for dispensing the curable filler material within the appliance trough. Typically, the filler applicator will be a dispensing gun capable of applying the PVS resin in a controlled manner through the nozzle which is attached to the gun. More typically, the kit will include two or more nozzles, where each nozzle will have a different tip diameter to dispense a different ribbon size of the filler to most efficiently fill target locations of differing sizes. Further optionally, the kit may include two or more cartridges or other containers of the curable filler material, where the materials have different properties, such as color. Still further optionally, the kit could include one or more coloring materials to permit the clinician to mix and color the filler material at the time of use. In addition, the kit may include one or more shaping tools which permit precise sizing and shaping of the pontic. For example, the kit may be provided with a spatula for sizing and shaping the material before it is cured. Alternatively or additionally, the kit may comprise a knife, grinder, or other tool for shaping and removing the filler material after it has cured. To facilitate the fabrication of dental pontics in a manufacturing setting, the curable tooth-colored silicone rubber catalyst- and base-paste may be supplied in foil bags and precisely dispensed from a Pentamix system eliminating either hand-mixing or dispensing with a hand held dispensing gun.
In a third aspect of the present invention, improved methods for repositioning teeth after extractions or impatience with substantial gaps between adjacent teeth are provided. The improvements are in methods for repositioning teeth which use polymeric shell appliances each of which have a trough for receiving and resiliently repositioning the teeth, e.g., as in the Invisalign(copyright) System commercially available from Align Technology, Inc., assignee of the present application. The polymeric shell appliances have different geometries and are worn successively by a patient to reposition the teeth in a number of stages. The improvement comprises providing at least some of the polymeric shell appliances, also referred to as aligners, which have pontics at a location within the appliance trough which will fill a gap between teeth when the appliance is worn. Usually, each appliance worn will have a pontic at the location of the gap, and the size of the pontic may be decreased as the treatment progresses and the width of the gap closes. In addition to the esthetic benefits described above, the provision of a pontic within the gap as the teeth are being closed is believed to provide therapeutic benefits as well. In particular, the presence of the pontic will reduce or eliminate the tendency of teeth which are being closed over a gap to tilt or incline into the gap. Thus, it is expected that teeth which are treated with the polymeric appliances to close such gaps will remain generally more upright as they are moved, thus reducing or eliminating the need to correct any tilt or inclination which is induced by the treatment.